1. Field of the Invention
This invention relates to catalysts for fluid catalytic cracking which produce high octane gasoline and increase light (C3 and C4) olefin yields, while minimizing the gasoline yield loss typically associated with octane additive systems. The catalysts employed are composed of a mixture of zeolite Omega (ZSM-4) and a Y zeolite in a conventional catalyst matrix.
2. Description of Previously Published Art
For many years, cracking catalysts employing some form of faujasite type Y zeolite have been used to produce high octane gasoline in the fluid catalytic cracking (FCC) process. Catalysts employing said zeolite in a matrix are disclosed in U.S. Pat. Nos. 3,140,249, 3,352,796, 3,647,718, 4,581,341 and 4,493,902. Recently, several disclosures have appeared which use mixtures of zeolite Y with other components to improve the octane of the resulting gasoline-range product. U.S. Pat. Nos. 3,758,403, 3,894,931, 3,894,933, 4,289,606, 4,309,279, 4,309,280 and 4,368,114 disclose the use of zeolite Y admixed with zeolite ZSM-5 in the FCC catalyst particle or the use of a mixture of two FCC catalysts, one a conventional cracking catalyst using Y and the other using ZSM-5, or the use of a conventional FCC catalyst with finely powdered ZSM-5 added to the charge stock to make higher octane gasoline. U.S. Pat. No. 4,340,465 discloses the use of a FCC catalyst employing a mixture of Silicalite and rare-earth-exchanged Y to make a higher octane gasoline. U.S. Pat. No. 4,137,152 discloses the use of catalysts composed of a mixture of Y and Mordenite. U.S. Pat. No. 4,740,292 discloses the use of catalysts composed of a mixture of zeolite Beta with a conventional zeolite Y cracking catalyst and European Patent No. 350,331 discloses the use of mixtures of zeolite L with zeolite Y catalysts, both for improved gasoline octane. However, in all cases there is a gasoline yield penalty associated with the production of high-octane gasoline.
The synthesis and composition-of-matter of zeolite Omega (also known as ZSM-4 and LZ-202), the synthetic counterpart of the natural mineral Mazzite, has been described in several patents (U.S. Pat. Nos. 3,923,639, 4,021,447, 4,241,036, 4,331,643, 4,840,779, U.K. Patents 1,117,568, 1,297,256, 2,175,890, European Patent 273,403 and World Patent 87/00158) and in numerous articles in the open literature, including Perrotta, et al, Journal of Catalysis, Vol. 55, pages 240-249 (1978).
The stabilization procedure used for the Omega zeolite of the present invention is one commonly applied to zeolite materials, utilizing ammonium exchanges, hydrothermal treatment and acid extraction. Its application to zeolite Omega is described in U.S. Pat. Nos. 4,724,067 and 4,780,436. An alternate approach to stabilization is presented in U.S. Pat. No. 4,503,023 and involves treatment with ammonium hexafluorosilicate to selectively replace framework aluminum with silicon, thus stabilizing the structure.
The use of a catalyst comprising a mixture of an Omega zeolite with a Y-type zeolite is disclosed in U.S. Pat. No. 3,864,283, while the use of zeolite Omega as a catalyst for FCC has been described in U.S. Pat. No. 4,724,067. However, no claims are made concerning the use of stabilized zeolite Omega in conjunction with a Y zeolite as a catalyst for production of improved-octane gasoline.
3. Objects of the Invention
It is an object of this invention to use a stabilized zeolite Omega as an effective catalyst or additive to increase the octane of FCC gasoline which is produced without the use of external hydrogen pressure.
It is further an object of this invention to produce and use a dual catalyst which is a combination of a stabilized zeolite Omega and a Y zeolite for increasing the octane of FCC gasoline as well as increasing the olefinicity of the light gas product.
It is further an object of this invention to produce and use a composite catalyst consisting of a stabilized zeolite Omega, a Y zeolite (rare-earth exchanged and/or ultrastabilized), a matrix and a binder as a very effective catalyst or additive for increasing the octane of FCC gasoline as well as increasing the olefinicity of the light gas product.
These and further objects will become apparent as the description of the invention proceeds.